5.7 OMC cobra starting problems

[Mazda3GT]

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Hi there, I have a 1989 5.7L omc cobra all mechanical engine ( no electronic egnition or choke, has points and condensor etc...) I feel the problem may be due to weak spark. The last time the engine was running i had it idling and i noticed the tach gauge to be bouncing up and down about a 400 rpm gap, this was when it was idling with a little throttle (1200 rpm) I let the engine warm up, then I shut it off, came back a few hours later ready to go out and it wouldnt start. Turned over fine, but wouldnt catch, could smell gas so i doubt gas is the issue, I'm aware of flooding engines. I think the coil may be the issue I will check out what was suggested in this post when i go back up to the boat on the weekend. But what else do you think the problem could be? Thanks for your time.

Steve
1989 Doral Concept

 

[wire2]

Re: 5.7 OMC cobra starting problems

Pull a couple of plugs & look at tip. Wet? Oily?
Then pull coil wire from distributor, hold it near block with insulated pliers, crank engine.
?" or longer blue spark?

 

[Haut Medoc]

Re: 5.7 OMC cobra starting problems

A bad tach can ground the points......
Disconnect the tach at the coil & see what happens...
This is a 5.7 GM or 5.8 Ford?.....​

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

It is a 5.7 GM block, and I will try that next time I'm at the boat.

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

Okay, I have disconected what i believe to be the tach wire from the distributor, this wire was attahced to the back of the points. With that wire off the motor still had no spark while turning over. I was testing for spark by taking the main wire feeding the distributor and holding it close to the block and looking for spark (there was none) I tried it at various distances away from the block, and made sure it was a good grounding point, but still no ark at all while it was turing over. I tested the coil for voltage, the readings i got were 5 volts from the positive terminal of the coil to the negative terminal of the coil while the key was in the run position. I got the exact same reading as the motor was turning over. I checked the negative terminal of the coil to ground and read zero, so I dont think there is any backfeed or short circuit. I also checked the postive terminal of the coil to a good ground and came out with the same reading basically (within .5 volts) . Any more ideas? I'm heading up to the boat tomorrow morning. Thanks for your help.

Steve

 

[Boatin Bob]

Re: 5.7 OMC cobra starting problems

Sounds like the wire you pulled off the coil was from the points, you'll never get a spark with the points disconnected. There should be 3 wires on the negative post, black from the points (leave this on) and 2 gray wires, one from the tach and one from the ESA. Go ahead and pull both of them off and check again. Also using your meter go on the positive side of the coil and put the other lead on engine ground, while turning over you should have much closer to 12v at the coil, if not try taking a jumper wire direct from the battery to the coil and try to turn it over.

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

There was only the one black wire entering the distributer through a little black rubber gromit. No other wires were in the distributer. I did notice that there were multiple wires on the coil however, maybe a grey and a purple and red I think. I will try and jump a positive wire directly for the batter to the coil and see what happens. It wont hurt feeding the 12 Volts when the engine is running will it? Thanks again.

Steve
Port Severn Ontario

 

[searay3]

Re: 5.7 OMC cobra starting problems

The black wire from the neg side of the coil belongs on the insulated side of the points. The grey wire is the tach wire. Remove all wires from the neg side of the coil except the black one, leave that connected. Turn on the key and with a meter check for 8+ volts at the POS side of coil. If there is power there, pull the coil wire and check for spark while cranking the engine. If it returns, inspect the rotor and cap looking for anything abnormal. Cracks, burns, corrosion etc. If all looks good put the rotor and cap back on and check for spark at the plugs. If there is spark and the point gap is set correctly, it should fire. Do you have a manual for your drive package? You really do need one if you will be doing the work on your motor/drive.

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

Ok I was at the boat today and tried a few new things. First things first I had a hunch it was a coil so I replaced it, $70 later I found that wasnt the problem. When the boat was cranking over I got 10 volts to from the positive side of the coil to ground. When the key was in the run position I got 5 volts. I do have a spark tester screw driver and it was pretty close to dark so it was easily spotted. Anyway I noticed I was getting spark at the begining of the crank over and the end of the crank over, but nothing in the middle. Even when i held it cranking over for 3 to 5 sceonds, only in the start and end did I ever see spark. I dont have a proper engine service guide yet, but do have the manual the boat came with. So no I do know where the tach wire is. Your right the two grey wires on the negative side of the coil are for the tach (1) and the other to an ESA module. Tomorrow I will be heading back to the boat and I will remover the two gray wires and see what happens. Should it start I will find out where the problem is, Tach or ESA module. Thanks Again.

Steve

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

I removed the two gray wires yesterday from the coil and left the black one remaining. The engine did not start. I was doing this at night time, completely dark, so I used my spark tester screwdriver and noticed this about the spark: When the key was turned from off to the run position there was a sinlge spark, while remaining in the run position no more spark. When the key was turned from run to start there was a single spark when the engine began cranking then no more spark while cranking, and finally one more spark when the key was released and stopped cranking. Could this possibly be a bad key switch? I noticed that the gray wires dis-engaged the tach and the ESA thingy OMC has, so I think those would be ruled out as a probable cause.

Thanks,
Steve

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

Anybody Got anything new for me to try???

 

[imported_TheMan]

Re: 5.7 OMC cobra starting problems

Connect a remote starter to the starter solenoid if you are worried about the key switch..

 

[Boatin Bob]

Re: 5.7 OMC cobra starting problems

CAn't be the ignition switch as all it does is energize the start assist solenoid and it must be doing that or the engine wouldn't crank at all. The assist solenoid also feeds 12v to the pos side of the coil. At first I thought you were missing this feed but one of your last posts said " When the boat was cranking over I got 10 volts to from the positive side of the coil to ground. When the key was in the run position I got 5 volts." so that appears to be working. I would go back and really check those points to make sure they are clean and gapped right, also grab the rotor and try to move it, possibly the distributor bearings are worn and the shaft is sloppy? With the dist cap off either have someone crank or you put a socket on the crank and turn the engine and watch the points. are they really opening and closing?

 

[MikDee]

Re: 5.7 OMC cobra starting problems

Not sure about the wire colors on the coil, but here's how it works for points, the black wire off the coil goes to the points for spark (to run). Usually there is a tach wire on this coil terminal also (maybe gray). Now, on the other small coil terminal, there is one wire from the ignition switch that is for ignition (run) it is a resistor wire to keep the points from burning up, it may show lower current on a meter. The next wire on this same terminal is from the ignition switch for starting only (switch start position) it gives full voltage (power) to the points only while cranking, when you release the switch it should have no power to it.

 

[Zero Balance]

Re: 5.7 OMC cobra starting problems

the Yellow/Red wire is from your starter solinoid. This will give you 12v to your +coil while cranking. Check voltage. The purple wire will be coming from your Voltagte Regulator to the +coil. This supplies your lower voltage (around 9 volts I think) to the coil while running.

Check your points again. Check the continuity between thew points to be sure you circuit is closing. If you have 12v in the run position going through your coil and your coil is ruled out as defective your dist is the next link in the chain. Replace your condensor and points after you've gone through these. i think thats all thats left.

sorry for the repeat..lol

 

[Mazda3GT]

Re: 5.7 OMC cobra starting problems

Hey everyone, I would like to thank everyone for the priceless advice, the problem was a bad condensor. I'm kind of glad the whole thing happened, even thought it cost me a few weekends of boating, I learned alot in the process, I think I will randomly start reading threads and learning more since you guys are all so knowledgeable.

Thanks again.

Steve

 

[imported_TheMan]

Re: 5.7 OMC cobra starting problems

Glad you were able to find it out.

Always be sure to take the key out of the ignition before doing any work on the ignition components -- it is a sure way to fry the condenser if you leave the key in the run position. (Did that one myself on accident after tuning the engine.. doh)